Add button to add action if one does not exist

What does this MR do and why?

Add button to add action if one does not exist

• if no action exists, add button to add one
• do not add a remove button yet
• update tests
• remove button will be added in another MR

Changelog: added

EE: true

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Note: Don't worry about not seeing the Override project approval settings header. That is behind a feature flag

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Upload a GitLab Ultimate license
2. Navigate to a project/group => Secure => Policies => New policy => Scan Result Policy => yaml mode => Copy/paste the below yaml in the editor

type: scan_result_policy
name: ''
description: ''
enabled: true
rules:
  - type: ''

3. Verify the actions section shows the New action button
4. Click the New action button
5. Verify the new action appears and the New action button appears

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #421920 (closed)